Diesel particulate filters are one of multiple components used to control emissions produced during the operation of diesel engines. The diesel particulate filter removes particulate matter, or soot, from the exhaust gas of a diesel engine. While diesel particulate filters have commonly been used in on-highway truck applications in the U.S. since 2007, their use in larger diesel engines, such as in off-highway equipment, locomotive and marine applications are relatively limited. Regulatory changes, however, have reduced the allowable levels of particulate matter in exhaust from new engines over certain duty cycles using certain testing procedures. This reduction is now fostering the use of diesel particulate filters in relatively large engine applications.
Two types of diesel particulate filters, partial flow (or flow through filters) and wall flow filters, are generally available. In flow through filters exhaust gas is directed through a metal fiber fleece by scoop shaped metal foils. The particulate adheres to the metal fleece. The filtration efficiency of such filters is understood to be in the range of 40 percent to 60 percent. Wall flow filters include channels having closed inlets with open outlets and channels having open inlets with closed outlets, the porous channel walls being formed filters. Exhaust gas enters the open ended channels and passes through the filter walls into channels having open outlets. The filtration efficiency of wall flow filters is understood to be greater than 90 percent. However, for a given area, wall flow filters exhibit a greater backpressure as compared to partial flow filters.
A number of technical challenges are faced when high filtration efficiency, wall flow, diesel particulate filters are applied to off-highway, locomotive or marine applications. For example, one challenge is that standard wall flow diesel particulate filter elements, produced today for typical on-highway or off-highway applications, will only handle 350 to 400 horsepower (HP) per diesel particulate filter element. Another challenge is that simply scaling up diesel particulate filters for 350 HP to 400 HP trucks to those necessitated by 2,000 HP to 8,000 HP off-highway, locomotive, or marine engine applications result in wall flow filters that are larger than what can be produced with today's manufacturing technology.
To overcome such challenges multiple large wall flow diesel particulate filters sized at 350 to 400 horsepower per filter element have been employed in a single large housing or in a gang of single element housings. In both cases the diesel particulate filter elements are mounted in parallel, so that they can handle the high exhaust flow rates. However, such housings often are too large to practically fit in a locomotive car body, marine engine compartment, or off-highway equipment body.
Other potential issues include the plugging of diesel particulate filters due to an increase in the rate of particulate matter generation under certain operating conditions. Accordingly, there remains a need to improve upon diesel particulate filtration systems and particularly systems used in applications, such as off-highway, locomotive and marine applications, where changes in operating conditions may substantially alter the performance of the filters.